Cover the dried mushrooms with 1 cup of very hot water. Let stand until softened, about 20 minutes. Using a sharp knife, cut off the artichoke stems and peel off the dark outer leaves near the base. Cut off the crowns to within 2 inches of the base and trim off the dark skin from the artichoke bottoms. Scrape out the hairy chokes with a spoon and cut each artichoke into quarters. Cut each quarter into 1/8-inch-thick slices and add to a bowl of water mixed with 3 tablespoons of the lemon juice. Remove the porcini mushrooms from the soaking liquid and finely chop them. Carefully pour the soaking liquid into a bowl, stopping when you reach the grit at the bottom. Stir in the tomato paste until dissolved. In a medium skillet, bring the chicken stock to a boil. Add the chicken breasts, cover and simmer over low heat for 8 minutes. Remove from the heat and let stand covered. In a large nonreactive saucepan, heat the oil. Add the mushrooms, onion, garlic and 6 tablespoons of the parsley and cook over moderately high heat, stirring, until the vegetables are soft and aromatic, about 5 minutes. Drain the artichokes and pat dry. Add them to the saucepan and season with pepper. Cook, stirring occasionally, for 5 minutes. Remove the chicken breasts from the stock. Cut them into thin strips, about 1/8 by 1-1/2 inches long. Add the stock and mushroom liquid to the saucepan and bring to a simmer. Stir the flour into the white wine to make a slurry and stir it into the saucepan. Simmer for 10 minutes. (The soup can be prepared to this point up to 3 days ahead. Refrigerate the chicken separately. Reheat the soup before proceeding.) Add the chicken to the soup, season with salt and pepper and cook until heated through. Stir in the remaining 2 tablespoons chopped parsley and lemon juice to taste and serve hot. 6 Servings soup 59